Some conventional photovoltaic units have intrinsic (i-type) amorphous silicon interposed between an n-type crystalline silicon substrate and a p-type amorphous silicon layer. The structure reduces defects at the interface, thereby improving heterojunction interface properties of such devices. These types of photovoltaic units are called heterojunction solar cells.
PCT International Application Publication, No. WO2013/133005 discloses a heterojunction solar cell in which there are provided: n-type amorphous semiconductor strips and p-type amorphous semiconductor strips on a back face, which is opposite a light-receiving face; and n-electrodes and p-electrodes respectively on the n-type amorphous semiconductor strips and the p-type amorphous semiconductor strips (hereinafter, will be referred to as a “back face heterojunction solar cell”).